Damage of Coated Turbine Blades after Overheating Events

miscellaneous

English

Turbine blades of aircraft engines are the most loaded parts owing to the high working temperature, induced mechanical stresses as well as an abrasive and corrosive environment. The metallic coatings on blades serve as physical barriers protecting the underlying substrate from these severe degradation effects. One of the most serious degradation modes of coatings is their creep degradation during overheating events. If the critical temperature of gases becomes significantly higher than the nominal one, the surface layer of the blades suffers from initiation of microcracks and cavities in a very short time. Growing of these defects then leads to spalling and progressive destruction of the coating during the further service. This article presents examples of coatings on rotor blades of high-pressure turbines in aircraft engines that were degraded after overheating events during the service. These diffusion aluminide coatings are based on the intermetallic compound beta-NiAl that forms under the influence of the substrate (nickel superalloy). The damage of coatings is demonstrated by identification of cracking and spalling initiation on metallographical samples prepared from blades of two engines that experienced different kinds of overheating.

gas turbines, blade coatings, overheating, damage assessment

KIANICOVÁ, M.; POKLUDA, J.

14. 11. 2011

CMRDI & ESLIA

Luxor

692

700

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